Substrate Preparation and Treatment Methods

Substrate Surface Cleaning—Prior to any further processing such as surface analyses or surface treatment, all substrates were cleaned with lint-free tissues soaked with isopropyl or ethyl alcohol and subsequently stored at ambient labo­ratory conditions, i. e.,: 20 ± 2°C and 50 ± 5 % relative humidity.

Substrate Activation—Surface activation of polymeric substrates was car­ried out by the use of corona discharge treatment. It was performed with a Tan – tec EST unit, model HV 2010 (maximum power output of 1 kW and an output frequency range of 13-30 kHz)[25]

The system comprises the following key modules:

• High-frequency generator HV 2010 240 V/50-60 Hz,

• High-voltage transformer HT 10-28 kV output,

• Conveyor: controlled treatment speed 0.1-70 m/min.

In this work, the distance between the substrate surface and electrode was maintained at a constant 2.5 mm, whereas the treatment speed and energy out­put were controlled to achieve energy outputs, Eu, from 76 to 755 mJ/mm2 (Eq 8).

Alternative means for surface activation are the UV irradiation or flame treatment. The latter is carried out using an Aerogen[26] or Arcotec[27] flame- treatment units fuelled with natural gas. The stochiometry of flame is controlled by tuning the excess content of oxygen in the “after-burn" flame at the level of 0.4 to 1.5 %, while the intensity of flame activation is controlled by adjusting the flow rate of air (220-360 L/min).

The flame-activation conditions used in this work are as follows:

• Treatment speed: 60 m/min,

• Oxygen excess content: 1.4 %,

• Substrate surface-burner distance: 20 mm.